An auxiliary power unit (APU) is used to provide a power source for a vehicle cabin compartment such that heating, cooling, and/or electric power can be supplied to the cabin compartment without requiring the vehicle engine to be running. Thus, for example, the use of an APU eliminates long idling at truck stops, which in many situations could be as long as ten to twelve hours.
When used in such an application, the APU creates only the power required to run a heating, ventilation, and air conditioning (HVAC) unit for a driver who may be resting in the cabin compartment. Additionally, the APU provides assistance for the vehicle engine during cold-starts by heating up the engine block.
Typically, APUs are small diesel engines that are battery based. Further, most APUs are configured as burners such that only heat can be provided and not cooling. These diesel engines are expensive, heavy, fuel inefficient, noisy, and generate significant amounts of pollution.